Double-disk slide valves of this kind are known and are available in the form of flat, oval and round slide valves. Double-disk slide valves are generally used when it is required to seal the throughflow space of a slide valve relative to the remainder of the housing interior when the slide valve is in the open position. This is particularly the case when a stream of gas with contaminants of subliming substances is involved, because such contaminants can otherwise accumulate in non-sealed parts of the housing and may result in a blockage and accordingly may impede the operation of the slide valve. Double-disk slide valves are used for the same or similar reasons in the case of dust-containing gases or in the case of severely contaminated liquid media, such as, for example, in coal gasification plants, incineration plants, coking plants, chemical plants, pipelines and the like.
As mentioned above, double-disk slide valves in accordance with the preamble of claim 1 are known. For example, DE-C-868 543 discloses a double-disk slide valve in which the bridging pipe is composed of a resilient corrugated pipe having sealing rings arranged at the ends. The bridging pipe is housed in a tubular housing component of a slide valve disk, which serves simultaneously as holding means and guide means for the bridging pipe. When the slide valve is in the open position, the sliding rings are pressed against the housing sealing seats by the resilience of the corrugated pipe and by the expanding action of a wedge device.
That known structure has the disadvantage that in order to achieve a sufficiently good seal the bias of the resilient corrugated pipe has to be relatively high. The consequence is that when the bridging pipe is displaced, its sealing rings slide along the opposing sealing seats of the slide valve housing with a relatively high contact pressure. This creates considerable friction between the abutting sealing faces, so that substantial operating forces are required to switch over the slide valve. The wear to the sealing faces is also correspondingly high.
In order to avoid those disadvantages, it is proposed in DE-U-800 8316 that the sealing rings of the bridging pipe be mounted on an extension of the actuator rod for the slide valve disk and be provided with a restoring device. The restoring device has rollers attached to the sealing rings, which rollers run on actuating bars mounted in the housing and having lead-in grooves for the rollers arranged in the region of the slide valve passageway. Such a combined expanding and releasing device is intended firstly to ensure reliable contact pressure of the sealing rings when the slide valve is in the open position and secondly to ensure that the bridging pipe is freely movable along the two housing sealing seats on actuation of the slide valve.
In the double-disk slide valve mentioned above, however, this is achieved only by a very high level of structural complexity. For example, it is proposed that the shut-off plates of the slide valve disk be provided with rollers which in the closed position run in the lead-in grooves of the actuating bars in order that, especially in the event of high differential pressures, the shut-off plates are displaced with the lowest possible friction and without damage to the sealing faces. In such a double-disk slide valve it is necessary for a large number of individual components to be matched to one another in respect of their sequences of movement, with the result that such a double-disk slide valve has to be manufactured with the greatest precision. A large number of wearing components and components requiring intensive maintenance, that is to say components that require separate cleaning after a predetermined in-use period, increase the cost of using such a double-disk slide valve.
A double-disk slide valve of the kind described above having a reduced number of components, which is intended to ensure an unaltered high level of sealing between the sealing rings of the bridging pipe and the associated sealing seats or the slide valve housing when the slide valve is in the open position, is disclosed in EP 0 450 646 A2. That double-disk slide valve has a bridging pipe having two sealing rings joined to one another by a compensator, the sealing rings being arranged to be pressed under resilient bias against the sealing seats of the slide valve housing when the slide valve is in the open position. The compensator comprises a wave-like curved pipe component having an indentation extending around its circumference, the wave-like curved pipe component extending as an outer pipe component coaxially around an inner pipe component which is rigidly connected only to one of the two sealing rings. The latter pipe component is movable axially relative to the other sealing ring. Such a structure has proved satisfactory but still requires a certain amount of maintenance, it generally being necessary to remove the entire bridging pipe from the slide valve for maintenance, which gives rise to great expense both in terms of personnel and in terms of long down times.